In some electrical grid-codes wind turbine generators are requested to supply reactive power even if they are curtailed to zero active power.
Wind turbine generators with power converter technology, and in particular, the full-scale type, those with the power converter connected in series between the stator of the electrical generator and the grid, have the capability to supply large amount of reactive power. This capability is highly desirable from a grid-stability point-of-view.
Wind turbines in a wind power plant are being coordinated through the SCADA or a power plant controller to act as a power plant. Here, the power plant controller can issue requests for both active and reactive power from the individual turbines in order to fulfill demands on plant level.
EP2693589 discloses a wind park control system for controlling reactive power output of wind turbines is described. The wind park delivers active power and reactive power to a utility grid. A total amount of reactive power required by the utility grid and an individual amount of reactive power for each wind turbine are determined. A capability scheme having an order for selecting the wind turbines to deliver reactive power is calculated based on the individual amount of reactive power and the total electrical power loss contributed by each connection of the wind turbines to the utility grid. An actual amount of reactive power provided by the wind turbines is adjusted. The reactive power output of each wind turbine is controlled based on the capability scheme. The wind turbines are selected for delivering reactive power in the order of the capability scheme so that the total amount of reactive power is fulfilled.
US2009218817 discloses a wind farm system is provided that is optimized for minimizing electrical loss. The wind farm system includes a plurality of wind turbine generators and a collector system including a conductor or network of conductors. The collector system also including a plurality of transformers with one or more transformers connected between each wind turbine generator and the conductors, and a substation transformer connecting the wind farm collector system to the electrical grid. The wind farm system also includes a monitoring system for monitoring the wind farm system electrical output and thermal condition, and outputs of the individual wind turbine generators. A control function may include voltage and real and reactive power commands to the individual wind turbine generators. The control function incorporates an algorithm whose technical effect is minimizing electrical losses for the wind farm system.